Right now, there are more than 2.5 million Americans living with breast cancer, according to the American Cancer Society. When a woman has breast cancer, doctors want to be sure the disease has not spread to her lymph nodes. It's one of the first places the cancer is likely to go, but now, they have a faster and easier way to target those lymph nodes.

Pamela Peterburs was healthy and fit when she found a lump during a self breast exam.

"I felt it, but I didn't think it was anything," Peterburs said.

Nothing turned out to be something.

"I admit when it was diagnosed I was shocked," Peterburs said.

She went to the Univeristy of California, San Diego to find out if her cancer had spread to her lymph nodes. Doctors there are using a new agent called Lymphoseek. It's a molecule that lets doctors find the lymph node.

"It specifically travels to the lymph node and binds to that receptor, and because of that, we can tag that to something we can see," said Dr. Anne Wallace, professor of clinical surgery at Moores UCSD Cancer Center in San Diego.

Radioactive particles target the lymph node and light up the area -- showing doctors which nodes require biopsies. Traditional techniques, such as blue dye, aren't as fast or exact. For patients, it can lessen the chance for extensive treatments.

"They determine if the cancer has moved to other areas, and if it has not, they do not have to go any further," Peterburs said.

Peterburs' cancer did not spread to her lymph nodes. She is now cancer-free and concentrating on her sister who was diagnosed with breast cancer soon after she was.

"It's frightening, and you go through a myriad of emotions, and I think that's what she is going through now, and I am trying to support her in any way I can," Peterburs said.

Getting outdoors and exercising is one bond that's helping them both.

"Four weeks after I had a lumpectomy, I ran a half-marathon," Peterburs said.

Doctors say another advantage of this new agent is that it leaves the body sooner than traditional blue dye. They believe Lymphoseek will also be used for other types of cancers, including melanoma.

BACKGROUND: According to the Susan G. Komen for the Cure Web site, a little more than 192,000 new cases of breast cancer are diagnosed in American women each year. From the 1940s until recently, the rate of new cases of breast cancer in the United States has increased by about 1 percent each year. Even though incidence has increased, mortality rates for white women have decreased. However, for black and Hispanic women, mortality rates have somewhat increased in the past 30 years.

WARNING SIGNS: Today, most women are diagnosed at the very early stages of breast cancer because of the increased use of mammography. However, not all breast cancers are picked up during a mammogram. Some of the most common symptoms are a change in the look or feel of the breast. These may include a lump that feels like a hard knot; swelling, warmth, redness, or darkening of the breast; a change in the size or shape of the breast; dimpling or puckering of the skin; itchy or sore breasts; nipple discharge that starts suddenly; and new pain in one spot that doesn’t go away.

WHEN BREAST CANCER SPREADS: When a woman has breast cancer, doctors want to be sure that the disease has not spread to her lymph nodes, which is the first place the cancer may travel. The lymphatic system is a network of vessels, ducts and glands that carry disease-fighting cells throughout the body. It can also act as a route for cancer cells to access the bloodstream. Doctors say the presence or absence of cancer in the lymph nodes is an important predictor of breast cancer prognosis and treatment. However, finding the right lymph nodes to test has not been easy for scientists.

LYMPHOSEEK: Researchers at the Moores UCSD Cancer Center in San Diego have conducted a new Phase III clinical trial of early-stage breast cancer patients. They found that a molecule designed to hone in on nearby lymph nodes is just as accurate as current techniques but is faster, more specific and easier to use. The molecule, called Lymphoseek, is a radiopharmaceutical that binds to the receptor on lymph node white blood cells. The radioactive portion of the molecule lights up, detecting sentinel nodes that are the most likely candidates for doctors to biopsy for possible cancer. Doctors have traditionally used blue dye to target these lymph nodes. However, the dye does not always go to only the sentinel nodes. Dr. Anne Wallace, professor of clinical surgery at the Moores UCSD Cancer Center, said Lymphoseek is easier to use than the blue dye and takes less time. The new agent is also cleared from the body faster. Wallace said Lymphoseek could standardize the process of lymph node mapping, making it easier for surgeons.